1. Field of the Invention
This invention relates generally to thermal exposure monitors, and more particularly to a cumulative thermal exposure monitor and system for reading the same. The time-temperature integrating monitor device has a thermally insulative housing with a cavity and a thermally-responsive member therein formed of shape memory material which may be coated with shape memory polymer that gradually changes from a first shape to a second shape over a prescribed temperature range wherein the thermal capacity and insulative properties of the housing, cavity, and shape memory material transition temperature range are correlated relative to one another and calibrated to closely match a thermal decay profile (time-temperature profile) of the product being monitored, and the data can be retrieved remotely via RF transponder technology without directly viewing the monitor device.
2. Background Art
It is of utmost importance to maintain processed produce such as food products and perishable non-food products such as medical products, drugs, research reagents, pharmaceuticals, human organs and tissues, etc., within a predetermined temperature range and to determine whether such products may have been exposed to detrimental temperatures outside of a specified temperature range during some step in the chain of distribution from the source to the destination.
The demand for processed produce and perishable non-food products has pushed the limits of the distribution systems of the perishable products industry to maintain an unbroken temperature controlled chain from field to consumer and industry. Many segments of the food industry utilize a Hazard Analysis and Critical Control Point system (HACCP), which is a world-recognized, common sense approach to food safety and prevention of food contamination.
The HACCP has outlined seven principles for food safety and prevention of food contamination: (1) Conduct a hazard analysis to identify potential hazards that could occur in the food production process; (2) Identify the critical control points (CCPs)—those points in the process where the potential hazards could occur and can be prevented and/or controlled; (3) Establish critical limits for preventive measures associated with each CCP; (4) Monitor each CCP to ensure it stays within the limits; (5) Take corrective actions when monitoring determines a CCP is not within the established limits; (6) Keep records that document the HACCP system is monitored and working correctly; and (7) Verify that the HACCP system is working properly through tests and other measures.
Existing HACCP programs in place at the processing end of the chain are not equipped with proper tools to monitor all of the critical control points (CCP's) in the cold chain, and temperature related problems can still occur throughout the distribution chain. Thus, there is a need for a device that can be used for economically monitoring the links in the cold chain, especially when perishable loads are broken up and re-distributed.
Temperature monitors and indicators are known in the art. There are several patents that disclose various temperature indicating devices.
Bradbury, U.S. Pat. No. 2,966,261 teaches a “snap-action” temperature-sensing device having a thermally responsive bimetallic inverted V-shaped spring (not shape memory alloy or polymer material), and a latch insertable into the device to temporarily hold the spring member in an initial position. The apex of the V-shaped spring serves as a pointer and indicia on the housing represent zones corresponding to the location of the apex to indicate the temperature of the monitored product.
Rogen et al U.S. Pat. No. 3,483,752 discloses a temperature monitor using a shape-memory alloy sensor disposed in a compartment in a housing preferably constructed of transparent acrylic plastic that has: (1) a thin wall section that is affixed onto the package of a medium being monitored to serve as a preferential heat conducting path between the monitored medium and the sensor is affixed onto the package of a medium being monitored, and (2) a thick wall section that serves as a preferential insulating path between the sensor and the ambient environment. The sensor must respond decisively (instantaneously) to a small temperature change and can be made to actuate (change shape) more rapidly than the monitored medium, to insure that the monitored medium (blood) is either safe or unsafe, but otherwise remains dormant. This device does not utilize a scale because there is no degree of spoilage of blood (it is either considered good or bad). It also requires the user to observe the configuration of the shape memory alloy sensor (whether it is straight or coiled, curled or flat, or twisted or flat) in order to determine whether the monitored medium has exceeded the specified temperature. This device differs from the present invention in that it is strictly a binary device (it can only give you a yes or no answer), it is designed to measure whether a temperature threshold has been exceeded, and its housing merely isolates the mechanism from its environment and links it to the medium.
Dewaegheneire, U.S. Pat. No. 4,448,147; Weynant nee Girones, U.S. Pat. No. 5,018,874; and Darringer et al, U.S. Pat. No. 5,076,197 disclose “step” type temperature monitors. These devices differ from the present invention in that they merely measure and indicate whether one or more temperature thresholds have been achieved.
Bianchini, U.S. Pat. No. 5,531,180 teaches a device utilizing a pre-loaded tension spring or leaf spring (not shape memory alloy or polymer) in cooperation with a fluid material having a controlled temperature dependent viscosity, wherein the viscosity changes as a function of temperature. The spring and fluid are located in a compartment in a transparent housing or case that is affixed onto the package of a medium being monitored. The end of the spring has an enlargement or indicator that is held in a first position by a removable retaining pin which is removed after the device along with the monitored medium has been frozen. As a result of the viscosity of the temperature dependent fluid or material, with the elapsing of time, the pressure of the spring will cause the indicator to move to a second position to indicate that the frozen product has gone through “thermal mishandling” in is unfit for consumption. The time required for the indicator to move to the second position is proportional to the viscosity and to the radius of the fluid friction surface (exterior surface of the spherical indicator) and inversely proportional to the elastic constant of the spring, which urges the indicator through the viscous medium. This device operates on different principles than the present invention and relies on the relationship of viscosity of a fluid with respect to temperature.
Shahinpoor et al, U.S. Pat. No. 5,735,607 discloses a temperature sensor having an indication surface, at least one shape memory alloy (SMA) member with a first shape at temperatures below a critical temperature and a second shape at temperatures above the critical temperature, and a plurality of indicators mounted with the members which obscure the indication surface when the members are in the first shape, and do not obscure the indication surface when the members are in their second shape. The shape change of the SMA element causes the sensor to change between two readily distinguishable states to indicate that a temperature threshold was exceeded, and must always be maintained at a temperature below the transformation temperature of the shape memory alloy member(s) until the beginning of the sensing operation.
Shahinpoor, U.S. Pat. No. 6,612,739 discloses a shape memory alloy temperature sensor having a sensing element with a portion made with a shape memory alloy mounted with a body fixedly at two ends. The fixed mounting at one end, is configured so that it can be converted to allow a moveable relationship between the body and the sensing element. While the mounting is fixed, the sensing element is prevented from indicating temperature deviations, and the apparatus can be stored and handled freely. After the mounting is converted to provide a moveable relationship, a temporary temperature excursion can cause the SMA portion to contract, providing a discernible change in the relationship between the sensing element and the body.
Shahinpoor, U.S. Pat. No. 6,837,620 discloses a shape memory alloy temperature sensor that provides a persistent indication that it has been exposed to temperatures below a certain critical temperature for a predetermined time period. An element of the sensor made from shape memory alloy changes shape when exposed, even temporarily, to temperatures below the Austenitic start temperature and well into Martensite finish temperature of the shape memory alloy. The shape change of the SMA element causes the sensor to change between two readily distinguishable states. The sensor includes a one-way stop element that creates a persistent indication of the temperature history, allowing the sensor to be manufactured and stored at temperatures above the Austenitic temperature without causing the indication of an over-temperature e
Waynant nee Girones, U.S. Pat. No. 5,335,994 discloses a temperature monitoring device having a casing made of synthetic material that contains a motor element with it a movement transmission element consisting of a piston and rod and a shape memory alloy spring acting on at least one indicator element irreversibly to record each overstepping of a predetermined threshold temperature. The device is capable of having a variable response time (“delay time”) on each of the temperature thresholds. One embodiment of the device enables the durations of the overstepping of the various temperature thresholds to be visually indicated.
Shah, et al, U.S. Pat. No. 6,509,094, discloses a polyimide coated shape memory material suitable for thermomechanical treatment to shape-set the material into the desired configuration and activate shape memory properties. The polyimide coating is subjected to a curing regime that imparts higher heat resistance in the polyimide coating to withstand the elevated temperatures required during the shape-setting treatment.
Transponder or transceiver type identification systems are also known in the art, and generally are capable of receiving an incoming interrogation signal and responding thereto by generating and transmitting an outgoing responsive signal. The outgoing responsive signal, in turn, is modulated or otherwise encoded so as to uniquely identify or label the particular object to which the transponder element is affixed.
Carroll, U.S. Pat. No. 4,857,893, discloses a transponder device that receives a carrier signal from an interrogator unit which is rectified by a rectifying circuit in order to generate operating power. Logic/timing circuits derive a clock signal and second carrier signal from the received carrier signal. This clock signal reads a unique identifying data word from a programmable read only memory (PROM). The data word is encoded and mixed with the carrier signal in a balanced modulator circuit. The output of the balanced modulator is transmitted to the interrogator unit where it is decoded and used as an identifying signal. The identifying signal identifies the particular transponder device from which it originated. The rectifier and balanced modulator circuits are realized from the same diode elements. All electrical circuits of the transponder device are realized on the same monolithic semiconductor chip, and in one embodiment, an antenna receiving/transmitting coil is also part of the chip, being placed around the periphery thereof.
Galasko, U.S. Pat. No. 4,578,992, discloses a tire pressure indicating device including a coil and a pressure-sensitive capacitor forming a passive oscillatory circuit having a natural resonant frequency which varies with tire pressure due to changes caused to the capacitance value of the capacitor. The circuit is energized by pulses supplied by a coil positioned outside the tire and secured to the vehicle, and the natural frequency of the passive oscillatory circuit is detected. The natural frequency of the coil/capacitor circuit is indicative of the pressure on the pressure-sensitive capacitor.
Dunn, et al, U.S. Pat. No. 4,911,217, which is hereby incorporated by reference herein in its entirety, discloses a RF transponder in a pneumatic tire. The transponder has two electrodes, a first of which is positioned such that the average spacing of the first electrode's surface from one of the tire's steel reinforcing components, such as an annular tensile member in its bead or a steel-reinforced ply, is substantially less than the average spacing of the second electrode's surface from the reinforcing component. This patent also describes an identification system (“reader”) that can be used to interrogate and power the transponder within the tire. The identification system includes a portable hand-held module having within it an exciter and associated circuitry for indicating to a user the numerical identification of the tire/transponder in response to an interrogation signal.
Schuermann, U.S. Pat. No. 5,451,959, which is hereby incorporated by reference herein in its entirety, discloses another example of a RF transponder that can be installed in the carcass of a pneumatic vehicle tire. The transponder system includes an interrogation unit for communicating with a plurality of responder units. The responder unit contains a parallel resonant circuit having a coil and a capacitor for reception of a RF interrogation pulse. Connected to the parallel resonant circuit is a capacitor serving as an energy accumulator. A processor may be provided for receiving input signals from a sensor which responds to physical parameters in the environment of the responder unit, for example to the ambient temperature, the ambient pressure or the like. The sensor could for example be an air-pressure sensitive sensor. In this case the responder unit can be installed in the carcass of a vehicle pneumatic tire and, with the aid of the interrogation unit contained in the vehicle, the air pressure in the tire can be continuously monitored.
Geschke, et al, U.S. Pat. No. 5,661,651, which is hereby incorporated by reference herein in its entirety, discloses another example of a wireless RF transponder for installation in a pneumatic vehicle tire for monitoring vehicle parameters, such as tire pressure. RF signals transmitted from different tires may be distinguished based upon the frequency of the transmitted signal. In order to sense the pressure inside a tire, tire pressure monitoring systems utilize a pressure sensor located within the tire.
Mehregany, et al, U.S. Pat. No. 5,712,609, which is hereby incorporated by reference herein in its entirety, discloses a micromechanical memory sensor that serves as a mechanical memory latch or sensor, the activation of which is triggered by a change of conditions, e.g., temperature, acceleration and/or pressure. The device has a latch member that mechanically latches upon detection of a threshold value of a variable condition (e.g., temperature, acceleration and/or pressure) and circuitry for detecting such latching, and further includes a resetting mechanism for electrically unlatching the latch member whereby the sensor latched purely mechanically is electrically reset for repeat use. This device is an example of a sensor that senses and indicates that a transient threshold or extreme value (i.e., over-temperature or over-pressure condition) has occurred. The transponder transmits tire identification and tire pressure data in digitally-coded form, and is “passive” in that it is not self-powered, but rather obtains its operating power from an externally-provided RF signal. The tire in which it is installed has two spaced beads, each including an annular tensile member of wound or cabled steel wire. The transponder antenna is positioned adjacent one of the annular tensile members for electric or magnetic field coupling to the annular tensile member.
Blama, U.S. Pat. RE 37,956, discloses a method of and apparatus for identifying an item to or with which a radio frequency identification tag is attached or associated. The tag is made of a nonconductive material to have a flat surface on which a plurality of circuits are pressed, stamped, etched or otherwise positioned. Each circuit has a capacitance and an inductance. The capacitance is formed from the capacitive value of a single capacitor. The inductance is formed from the inductive value of a single inductor coil having two conductive ends each connected to the capacitor. Each tag is associated with a binary number established from a pattern of binary ones and zeros which depend on the resonance or non-resonance of each circuit, respectively, and the circuits position with respect to the binary table. The binary number may be converted to a decimal number using the binary table for conversion.
A “temperature sensitive” product does not decay or become spoiled as a result of exposure to a given temperature; instead, it spoils due to the amount of heat imparted to it as a result of a temperature difference over time. In other words, a given product, such as a food product or produce, can safely tolerate short exposures to an elevated temperature, but not long exposures. Thus, prior art devices that merely indicate that a temperature threshold was achieved or exceeded at some point in time do not indicate the cumulative amount of heat energy absorbed within a preferred storage temperature range and whether, at any time, the cumulative heat energy absorbed has taken place for a period of time sufficient to cause any degree of deterioration based on the time and temperature thermal deterioration profile of the perishable product.
The present invention utilizes some of the components and technology described in commonly-owned U.S. Pat. No. 6,425,343 and U.S. Pat. No. 6,848,390, which are hereby incorporated by reference in their entirety to the same extent as if fully set forth herein. The prior commonly-owned patents disclose cumulative thermal exposure monitors that have a thermally-conductive housing adapted to be placed in close proximity to a product to be monitored and at least one thermally-responsive shape memory alloy member in the housing that has a first shape at temperatures below a critical temperature and a second shape at temperatures above the critical temperature and a transformation temperature range encompassing a prescribed time-temperature profile which is determined by the detrimental temperature related to the product being monitored. An indicator associated with the thermally-responsive member is moved from an initial position as the thermally-responsive member changes from the first shape to the second shape so as to be visually observed through a window on the housing to visually indicate whether the product being monitored has been exposed to temperatures above the prescribed detrimental temperature for a period of time that would be detrimental to the product. The present invention incorporates significant improvements in structure and operation over the previous commonly-owned patents, and the data can be retrieved remotely via RF transponder technology without directly viewing the monitor device.
The present invention is distinguished over the prior art and these patents in particular by cumulative time-temperature integrating thermal exposure monitors for monitoring heat energy absorbed over time and indicating the degree of deterioration based on a time and temperature thermal deterioration profile of a perishable product that has a known time and temperature thermal deterioration profile and is prescribed to be maintained within a preferred storage temperature range. The devices have a thermally-conductive housing with a fluid sealed interior cavity and a transparent window portion, the housing formed of a material having thermal capacity and insulative properties which moderate heat energy conducted therethrough over time. A thermally-responsive member movably disposed in the interior cavity is formed of a shape memory material and has a phase transition temperature range encompassing at least the preferred storage temperature range and has a first shape at temperatures below the phase transition temperature range and gradually changes to a second shape at temperatures in and above the preferred storage temperature range. The thermally-responsive member may be provided with an insulative coating or sheathing made of shape memory polymer or conventional elastomers that allows for multi-shape recovery and greater response lag. Either the thermally-responsive member or an indicator associated therewith is moved through the window portion from an initial position as it gradually changes from its first shape to its second shape. The thermal capacity and insulative properties of the housing material, cavity fluid, and shape memory material phase transition temperature range are calibrated relative to one another to function in mutual cooperation such that the housing moderates heat energy conducted therethrough over time and the thermally-responsive member absorbs the heat energy and gradually assumes its second shape upon absorption of heat energy over time to closely match the known thermal deterioration profile of the perishable product. The thermally-responsive member or indicator remains substantially in a position at which it was last moved, regardless of subsequent exposures of the shape memory material to lower temperatures, to indicate the cumulative amount of heat energy absorbed within and above the preferred storage temperature range and whether, at any time, the temperature has been above the preferred temperature range for a period of time sufficient to cause any degree of deterioration based on the time and temperature thermal deterioration profile of the perishable product. In a remote indicating embodiment, radio frequency (RF) transponder technology is used to remotely retrieve cumulative thermal exposure and identification data whereby the data can be retrieved remotely without directly viewing the monitor device, or removing it from the product package, and thereby allow monitoring in situations where it is difficult or inconvenient to visually check each monitor.